#4 username collisions

[Taso Lyristis]

handle username collisions gracefully.

idea #1: if a username collision occurs, one of the clients MUST change usernames before they may talk to anybody. e.g., the server will reply with a friendly, "change your name or die" message to the client to any command besides a /signon (or a new name-change command?)

[Jonathan Ellis]

Logged In: YES
user_id=657828

two parts:

* if auth is granted, the server will kick off a currently existing user w/
same name. this takes care of people forgetting to sign off from work,
then signing on again at home.
* so, the auth classes will pad names with numbers in the event of a
collision when allowguests is on to prevent this.